The invention relates to a method for metering fluid polishing agents according to the preamble of claim 1, and a metering apparatus according to the preamble of claim 8. It is known to apply fluid polishes either by high-pressure or by low-pressure methods, either continuously or intermittently to polishing wheels. The term, xe2x80x9cpolishes,xe2x80x9d as used herein, is to be understood to mean suspensions of abrasive solids in liquids, which may also be emulsified. xe2x80x9cPolishesxe2x80x9d also include grinding agents, inasmuch as the transition from grinding to polishing is seamless. In like manner, the term xe2x80x9cpolishing wheelsxe2x80x9d is to be understood to signify flexible, absorbent grinding wheels which consist of textile materials.
Disadvantages of conventional high-pressure apparatus consist in the fact that the application of polish is irregular, resulting in an uneven polishing process and in severe wear on mechanical parts of the polishing machine. Furthermore, considerable imbalance of the polishing wheels has been observed, resulting in damage to the bearings of the polishing shaft. Disadvantages of the low-pressure apparatus of the prior art consist in severe turbulence of the polishing agent, produced by the air turbulence caused by the polishing wheels, with the result that the area surrounding the polishing machine and the polishing machine itself become very contaminated, and that a great percentage of expensive polish is lost. Polish that has not been absorbed by the polishing wheels and/or flung away by the latter cannot be reused due to contamination of the polishing agent itself. Therefore additional waste matter is produced which has to be disposed of with difficulty and at great expense.
German patent DE 22 42 030 C3 discloses a high-pressure metering gun of very complex design for the application of polishing agents, in which the pressure of the polishing agent that is present in the polish chamber serves for the automatic control of the valve body and its piston rod which have the action of a differential pump. The continuous delivery of polish provides for a periodical pressure increase to which the differential piston yields after a time by letting a specific amount of the polish exit through the nozzle. This causes a pressure drop which in turn leads to a closing of the valve body. Therefore periodical pressure and spraying pulses continually develop with time-related intensity and velocity variations. This can also be described by saying that the metering constantly fluctuates between a high-pressure feed and a low-pressure feed, resulting in an alternation of the disadvantages of both kinds of metering. The frequency of the metering pulses amounts to around several Hertz.
To be able to vary the integral rate of flow of the polish, the differential piston according to DE 22 42 030 C3 is under the action of a compression spring whose bias can be varied by an adjusting knob provided on the feeding gun. In the case of a linear array of polishing wheels, since this knob moves along with the feeding gun, changing the adjustment is difficult if not even impossible without shutting off the gun. It is especially impossible to periodically stop and start the gun according to its location as it crosses intervals between the polishing wheels, so that the above-described contamination of the polishing machine and its surroundings occurs, with its likewise described consequences.
Through DE 37 28 714 A1 it has become known, in the case of an intermittently operating high-pressure metering apparatus for polishing paste, to feed this polishing paste at a low, undefined pressure, which can also be no more than a hydrostatic pressure, to a reservoir chamber of the smallest possible capacity disposed in the housing ahead of the nozzle. The high pressure is produced by the timed operation of a compressed-air piston of large diameter which acts on a plunger of considerably smaller diameter, which thereby constitutes a second (differential) piston for the nozzle which has its own, spring-loaded ball valve. When the response limit of this ball valve is exceeded it opens, and after ejecting a portion of the polish it closes again automatically, i.e., the operation of the known apparatus is substantially controlled by pressure. The movement of the metering apparatus relative to and transversely across the polishing wheel is not described any more than is the distance-related and synchronized actuation of the metering device as it crosses over the polishing wheel. The known apparatus is also surprisingly unsuitable for such synchronization, because it operates too sluggishly on account of the pressure-dependent movement of the two pistons. On the basis of the problem to which it is addressed, the known solution offered deals with the entirely different problem of automatic supervision of all the important operations within the metering apparatus by means of a pressure sensor and an end-position sensor for the compressed-air piston, but it does not specifically deal with the positioning of the metering device. DE 1 997 213 U discloses an apparatus for the movement of at least one nozzle for grinding and polishing agents, and with means for the reversal of the nozzle(s) at the ends of the given maximum travel, which as a rule substantially exceeds the width of a polishing wheel, so that as the spraying process continues away from the polishing wheel a considerable amount of the polish is lost and the machine and its surroundings are contaminated. The solution offered deals, on the basis of the stated problem, with the entirely different problem of preventing the penetration of grinding and polishing agents into the drive and guidance mechanism of the nozzle(s) by encapsulation. No distance-related synchronization of spray cycles is disclosed and none is addressed.
In the known apparatus and methods, spray nozzles are always used which produce an outspread stream of diffused droplets, which results in additional losses of polishing agent and in contamination of the polishing machines and their surroundings. In contrast, the invention is addressed to the problem of teaching a metering method and a metering apparatus which require little investment in apparatus and can be quickly adapted to various metering conditions. In particular, the metering process is to be accessible also to programming and/or remote control.
The solution of the stated problem is accomplished in the metering method according to the present invention. Such a method and such an apparatus require but a small investment in apparatus and can quickly be adapted to various metering conditions; in particular, the metering process can also be made accessible to programming and/or remote control. This brings it about that the application of the polish to the periphery of each polishing wheel is uniform, resulting in a uniform polishing process, and it prevents the unbalancing of the polishing wheels and premature wearing out of mechanical parts of the polishing machine.
Severe turbulence of the polishing agent is no longer seen, so that the surroundings of the polishing machine and the polishing machine itself become less severely contaminated and only a very small percentage of the expensive polishing agent is lost. Thus less special-class waste matter is generated so that disposal costs are reduced. This is especially the case when the nozzle is one which when opened produces a solid stream of the polish.
In case of an arrangement of polishing wheels in a linear array along which the metering apparatus travels, changing the setting is extremely simple and can be done without stopping. It is especially possible to shut off the metering apparatus periodically in the marginal areas of the polishing wheels and/or when passing over gaps between the polishing wheels, so that the above-described soiling of the polishing machine and its surroundings with the consequences described is eliminated. The feed rate can be influenced by the following parameters: nozzle geometry, valve body open time, and pressure in the polish chamber. All parameters are controllable individually and independently of one another, without manipulations at the nozzle head itself.
Pursuant to embodiments of the processxe2x80x94either individually or in combinationxe2x80x94it is especially advantageous if
the opening and closing times of the valve body are controlled by square pulses,
in a linear array of several polishing wheels spaced apart along a polishing shaft, at least one nozzle head is moved along the row substantially parallel to the polishing shaft, and if the valve body is opened when crossing a polishing wheel and closed when crossing the spaces,
the open time of the valve body from one polishing wheel to the other is varied, especially if the open time of the valve body is made to diminish from the first to the last polishing wheel while carrying the material being polished parallel to the polishing shaft,
the speed of the travel of the nozzle head is reduced while passing over the polishing wheels and increased while passing over the spaces between them, especially if the traveling speed of the nozzle head, when the material being polished is carried parallel to the polishing shaft, is made to increase from the first to the last polishing wheel.
It is especially advantageous in further embodiments of the metering apparatus if, either alone or in combination:
the valve body is connected with a control piston which is housed in a control chamber separate from the polish chamber, and if the control chamber is connected to a hydraulic pump which is controllable by an external timer,
both sides of the control piston can be acted upon by the hydraulic fluid,
the polish chambers and the control chambers are arranged in rows running in the direction of movement of the valve body and are sealed against one another,
the polish chambers and the control chambers are housed in a common cylindrical body,
the valve body is replaceable on the piston rod and cooperates with the nozzle.
the nozzle head can be made to travel by means of a driving device at least substantially parallel to a polishing shaft,
the nozzle head is connected to a control apparatus by which it can be moved along an linear array of a plurality of polishing wheels on a polishing shaft, and by which the nozzle head can be activated when passing over the polishing wheels and can be stopped when passing over the intervals between them,
the nozzle head is connected to a control apparatus by which the open periods of the valve body can be varied from one polishing wheel to the next, especially to a control apparatus by which the open periods of the valve body can be shortened as the material being polished is carried parallel to the polishing shaft from the first to the last polishing wheel,
the nozzle head is connected to a control apparatus by which the speed of travel of the nozzle head as it passes over the polishing wheels can be reduced and can be increased as it passes over the intervals, especially to a control apparatus by which the speed of travel of the nozzle head can be increased from the first to the last polishing wheel as the material being polished is carried parallel to the polishing shaft.
An embodiment and the possibilities for its use are further explained below with the aid of FIGS. 1 to 4.